High density storage disks are configured with layers of materials that provide the required data stability for storage. The magnetic properties of the media may be softened when writing to the disk to assist changing the bit state. Energy Assisted Magnetic Recording (EAMR) device or Heat Assisted Magnetic Recording (HAMR) technology provides heat that is focused on a nano-sized bit region when writing onto a magnetic storage disk, which achieves the magnetic softening. A light waveguide directs light from a laser diode to a near field transducer (NFT). The NFT couples the diffraction limited light from waveguide (WG), then further focuses the light field energy beyond diffraction limit down to a highly concentrated (nano-sized) near-field media heating spot enabling EAMR/HAMR writing to the magnetic storage disk. Inefficiencies in the NFT can have a negative impact on the power budget of the laser diode and the EAMR/HAMR system lifetime. Higher NFT efficiency allows for lower laser power demand, relieving EAMR/HAMR system requirement on the total optical power from the laser source, and results in less power for parasitic heating of the EAMR/HAMR head resulting for improved reliability.
The light waveguide may operate primarily in either one of the following modes to drive the NFT. In a transverse electric (TE) mode, the predominant electrical field component is in the transverse direction (i.e., side-to-side, x-axis) above the waveguide core. In a transverse magnetic (TM) mode, and the predominant magnetic field component is in the transverse direction (i.e., side-to-side, x-axis), while the predominant electrical field component above the waveguide core has a significant longitudinal direction (z-axis) component. Driving the NFT using a TM mode waveguide has the advantage of a strong electrical field in the direction along the waveguide for easier coupling to the NFT above the waveguide core. For EAMR/HAMR devices using laser diodes that produce a TE mode wave, a TE mode to TM mode converter is needed to energize a TM mode in a waveguide. An efficient NFT driven by a TE waveguide has the advantage of avoiding the TE mode to TM mode converter, which provides a more compact and higher efficiency light delivery system.